The present invention relates to a system for supplying electrical power to load, the power supply system being capable of delivering an output voltage to the load, from an input voltage coming from an electric power network, the power supply system including:                at least two input terminals and at least two output terminals, the input terminals being adapted to be connected to the electric power network and the output terminals being adapted to be connected to the load,        a converter capable of converting the input voltage into the output voltage, the converter being connected between the input terminals and the output terminals, and        a device for limiting the homopolar current that is likely to flow between the electric power network and the load.The invention also relates to a drive chain capable of being connected to an electrical network, comprising an electrical machine and such a power supply system of the electrical machine.        
The invention is applicable to power supply systems intended to be connected to an AC network or indeed to a DC network. The invention is applicable to power supply systems capable of delivering to the load an AC voltage or a direct current voltage.
From the document FR 2963509 A1, a power supply system of the aforementioned type is known. The power supply system includes a three phase rectifier connected to a three phase power supply network and a three phase inverter connected to the output of the rectifier, the inverter being adapted to deliver a three phase voltage to a load. The rectifier and the inverter are connected to each other by means of a DC bus, and the system further comprises a device for limiting the homopolar current that is likely to flow between the network and the load.
The rectifier includes controllable electronic switches capable of converting the three-phase alternating current supplied by the power network into a direct current delivered at the output of the rectifier, the switches being controlled by a control device capable of sending them control signals to said switches. The control device is capable of limiting the absolute value of the homopolar voltage to a value less than or equal to one sixth of that of the direct current bus voltage.
However, such a power supply system is necessarily connected to an AC network, and the homopolar current, although limited, sometimes has a relatively large value.
The object of the invention is therefore to provide a power supply system that makes it possible to further limit the homopolar current likely to be fed into the network.
To this end, the invention relates to a power supply system of the aforementioned type, wherein the device for limiting the homopolar current comprises a transformer connected in parallel with respect to the converter, between the input terminals and the output terminals, the transformer having a first electromagnetic coil and a second electromagnetic coil.
According to other advantageous aspects of the invention, the power supply system consists of one or more of the following characteristics, taken individually or in accordance with any technically possible combinations:                the first electromagnetic coil is connected between the output terminals and an electrical ground, and the second electromagnetic coil is connected between the input terminals and the electrical ground, the first coil and the second coil having the same direction of coil winding between the respective terminals and the electrical ground;        the limiting device further comprises at least a first passive element, the or each first passive element being connected between the transformer and a corresponding output terminal;        the limiting device further comprises at least one second passive element, the or each second passive element being connected between the transformer and a corresponding input terminal,        the electric power network is an AC network, and the converter is intended to be connected to the AC network without the presence of a transformer between the AC network and the said converter,        the converter is an AC-AC converter intended to be connected to an AC network, the AC-AC converter being capable of converting an AC input voltage, coming from the AC network, to an AC output voltage; and        the AC-AC converter comprises a voltage rectifier adapted to be connected to the AC network and a voltage inverter connected to the output of the voltage rectifier.        
The invention also relates to a drive chain adapted to be connected to an electric power network, the drive chain comprising a load, such as an electrical machine, and a power supply system for the electrical machine, wherein the power supply system is as defined here above.
According to other advantageous aspects of the invention, the drive chain includes one or more of the following characteristic features, taken individually or in accordance with any technically possible combinations:                the transformer has a transformation ratio between the second electromagnetic coil and the first electromagnetic coil, the or each first passive element has a first impedance, the or each second passive element has a second impedance, and the first and second impedances satisfy the following equation:Z1+K2×Z2=(K−1)×ZL where Z1 and Z2 represent respectively the first and second impedances,K is the transformation ratio, andZL represents the impedance of the load relative to an electrical ground;        the transformation ratio (K) of the transformer (36) satisfies the following equality condition:K=1+√{square root over (2)}; and        the value of the first impedance is equal to the value of the second impedance, the value of first and second impedances being preferably defined by using the following equality condition:        
            Z      ⁢                          ⁢      1        =                  Z        ⁢                                  ⁢        2            =                        1                      2            ×                          (                              1                +                                  2                                            )                                      ×                  Z          L                      ;
These characteristic features and advantages of the invention will become apparent upon reading the description which follows, given by way of non limiting example, and with reference being made to the accompanying drawings.